During recent decades, the growth of the plastics industry and ever-increasing use of polymeric materials has coincided with an increasing awareness and concern for the safety hazards, especially with regard to fire hazards of such materials. One result has been the development of various fire retardant polymeric compositions and fire retardant additives for polymeric compositions. In past years, the major emphasis in the development of such fire retardant compositions has been in the achievement of low burning rates. More recently, however, there has been an increasing recognition of the hazards of smoke generation during fire and the advantages of char formation in inhibiting combustion. Furthermore, it is now more generally recognized that low burning rates do not necessarily imply or result in low smoke generation or beneficial char formation. As a result, the need is now recognized for the development of improved fire retardant polymeric systems having not only low burning rates, but low smoke generation and high char formation.
Among the developments in the field of fire retardant polymeric systems in recent years, the development of polymeric systems employing antimony trioxide as a fire retardant additive has been outstanding. Antimony trioxide has been found especially effective for use in systems based on halogen containing polymers. The effectiveness of antimony trioxide, as well as other antimony compounds as a fire retardant additive to halogen containing polymers is generally recognized and has been described as a synergistic effect between antimony and halogen. Despite its generally recognized effectiveness in such systems, the use of antimony trioxide, as well as other antimony compounds, has been found to result in certain disadvantages. For example, although the use of antimony compounds has been shown in many instances to advantageously decrease flammability and burning rate of polymer systems, it appears to provide little advantage in inhibiting of smoke and in some instances has been found to increase smoke formation. In addition, in recent years, the rapidly rising cost of antimony compounds has been an economic disadvantage.
As a result of these disadvantages associated with the use of antimony compounds as fire retardant additives, considerable effort has been expended in a search for other fire retardant additives. However, the effectiveness of a particular fire retardant additive in a polymeric system is generally unpredictable and an additive useful and compatible in one polymeric system may be ineffective or even harmful with regard to fire retardance as well as other properties when used in a different polymeric system. Even more unpredictable is the effect achieved when fire retardant additives are combined. Combinations of various fire retardant additives may result in a beneficial or detrimental formulation with a given polymeric system. Furthermore, combinations of fire retardant additives may benefit one aspect of fire retardance and be detrimental to another.
It is known from The Journal of Fire and Flammability, 51-84, 1972, James J. Pitts, that in some instances at relatively high levels of addition, iron oxides or copper oxides may serve effectively as a partial replacement for antimony oxide in chlorine containing urethane foams. The use of iron or copper oxides in combination or in combination with antimony oxide at lower levels of addition or in other polymer systems is not shown.
It is also known from copending application Ser. No. 383,749, filed July 30, 1973, to employ iron compounds as fire retardant additives in polymer compositions prepared from halogen containing unsaturated polyester resins. In Ser. No. 383,747, filed July 30, 1973, it is disclosed that copper compounds can be advantageously employed as fire retardant additives in halogen containing unsaturated polyester resins. In copending application Ser. No. 490,423 it is disclosed that iron compounds may be advantageously combined with copper compounds and/or antimony compounds to provide a composition useful as a fire retardant additive in halogen containing unsaturated polyester resins. The polymeric compositions prepared in accordance with the aforementioned copending applications exhibit excellent fire retardant properties, including low smoke generation. However, it has now been found that substantial improvements in fire retardance and low smoke generation are achieved in such compositions when the halogen containing unsaturated polyesters are cross-linked with certain combinations of unsaturated monomers in a manner described hereinbelow.
Accordingly, it is an object of this invention to provide superior fire retardant polymer compositions based on unsaturated polyester resins that not only have low burning rates, but also exhibit low smoke generation when in contact with a flame.
It is also an object of the invention to provide superior fire retardant polyester resins that develop a beneficial, insulating layer of char in the presence of a flame which inhibits further combustion of the polymer.
It is still another object of the invention to provide polymer compositions based on unsaturated polyester resins wherein substantial improvements in fire retardance are achieved without diminishing or deteriorating other useful properties of the polymer system.
These and other objects are accomplished by this invention which is described in detail hereinafter.